In rail vehicles, it is known to deliver sand between the wheels and the rail in order to increase the adhesion of the wheel on the rail. This is done when the vehicle starts and on each occasion it is necessary to transit a high level of torque, with the sand being taken from a storage tank referred to as a “sandbox”. The sandbox is itself filled while the vehicle is stationary, in particular when it is beside a platform. The sandbox has a feed inlet orifice which is accessible from outside the vehicle.
In general, sandboxes are filled from a sand storage vessel connected to a feed pipe. The storage vessel is placed at a height that is sufficient to allow sand to flow under gravity into the pipe and then into the inlet orifice of the sandbox. In order to increase the rate at which sand flows, the storage vessel may be pressurized.
Proposals have already been made, in particular in documents DE 2 443 552 and EP 0 561 679 for devices for dispensing a granular material, which devices comprise at least one material transfer vessel fed with compressed air under pressure, and at least one portable dispenser head having one end connected by a flexible pipe to the transfer vessel. The pressure and flow rate conditions of the compressed air in the transfer vessel are determined so as to obtain a flow of material in the pipe.
The devices proposed by those prior documents are suitable for filling sandboxes when the inlet orifice is at man height, i.e. at a height that is low enough down for an operator on the platform to be able manually to insert the portable head into the inlet orifice of the sandbox. Such devices are suitable in particular for the European rail network.
In contrast, those devices are unsuitable for certain rail networks, in particular in North and South America, where rail vehicles are much taller and have large-capacity sandboxes with inlet orifices located near the top of the vehicle, i.e. orifices that are not directly accessible for an operator on the platform. Such sandboxes are filled, in known manner, with the help of a portable dispenser head having a shepherd's crook configuration, and can thus be referred to as a filler crook. It presents a rectilinear portion which is held by the operator, with said rectilinear portion being extended by a top curved portion that comes over the top of the vehicle, said curved portion itself being extended by an end portion for insertion into the inlet orifice of the sandbox.
As in the devices known in particular from documents DE 2 443 552 and EP 0 561 679, the granular material moves along the feed pipe of the filler crook because of the action of compressed air.
Given the special shape of the filler crook, it is not without some difficulty that the granular material is made to move under pressure. One difficulty consists in pockets of air forming in the feed pipe, where said pockets of air give rise to jolting in the crook while granular material is escaping through the open end of the pipe. These jolts travel along the entire length of the crook and can hinder or even injure the operator. Another drawback lies in the difficulty of passing granular material round the curved portion of the filler crook, where the curved passage can give rise to the granular material slowing down or even becoming blocked, which prevents the filler crook from operating properly. This drawback becomes more marked as the sandbox fills up and the volume of air that remains in said sandbox decreases. That explains why the pressure inside the sandbox rises. Consequently, the transport pressure increases, and transport becomes jerkier, so that granular material and dust can escape.